This invention relates to direct fired heaters. In one aspect the present invention relates to heat exchanger means for such heaters. In yet another aspect the invention relates to a multi-section heat exchange means in which the lower section is provided with a plurality of bare tube heat exchange members and the second section is provided with a plurality of extended surface heat exchange members. In yet another aspect the invention relates to a multi-section heat exchange means wherein the second section is provided with a gradually reduced internal cross-section towards its upper portion so that the velocity of gas flow there-through is substantially constant. In still another aspect the present invention relates to a multi-section heat exchange means having in addition to said lower section and said second section, at least one additional heat exchange section having a plurality of extended surface heat exchange members.